FIG. 11 is an exploded view of a conventional semiconductor device manufacturing apparatus of this variety.
As shown in the diagram, a substrate processing chamber 3 of the semiconductor device manufacturing apparatus 1 is partitioned into ceilinged cylinders by a quartz reaction tube 4, and substrate processing gas is led into the substrate processing chamber 3 from a gas supply tube 13 connected to the bottom of the reaction tube 4. A gas exhaust tube 14 is also connected to the bottom of the reaction tube 4, allowing gas used for substrate processing and the like produced by the reaction in the substrate processing chamber 3 to be exhausted, and a vacuum pump 11 as a pressure-reducing exhaust apparatus is connected to the gas exhaust tube 14 via an exhaust tube 231. An exhaust trap 8 is provided to the exhaust tube 231 upstream of the vacuum pump 11, and this exhaust trap 8 is designed to remove residual components from the gas used for substrate processing exhausted from the reaction tube 4, i.e., from the substrate processing chamber 3. Positioned on both sides of the exhaust trap 8 are an upstream valve 9 on the upstream side and a downstream valve 10 on the downstream side, and these valves are provided to the exhaust tube 231 in order to attach and remove the exhaust trap 8. Furthermore, pipe heaters 16 are attached to the gas exhaust tube 14 and the exhaust tube 231 in order to prevent the precipitation of residual components, i.e., reaction by-products in the gas used for substrate processing exhausted through the reaction tube 4, and to supply the entire amount of gas to the exhaust trap 8. The pipe heaters 16 are composed of, e.g., ribbon heaters or other such flat heaters, and are wound around the exhaust tube 231 and the gas exhaust tube 14 so as to provide heating to the area between the exhaust trap 8 and the connection with the reaction tube 4.
The apparatus for installing and removing substrates (wafers) 23 in the reaction tube 4 is configured primarily from boats 12 for installing a plurality of substrates, and a boat elevator (not shown) for installing and removing the boats 12 in the reaction tube 4. The boat elevator is disposed vertically below the reaction tube 4, and the boats 12 are mounted on the boat elevator. A flange (not shown) as a lid for opening and closing the opening of the reaction tube 4 is provided at the bottom of the boats 12, and the flange includes an O ring (not shown) as sealing means for firmly bonding and sealing the flange to the peripheral edge of the opening of the reaction tube 4.
When a film is formed on the substrates 23 with the aid of the semiconductor device manufacturing apparatus 1, the boats 12 are mounted on the boat elevator, and the rising of the boat elevator causes a substrate 23 to be inserted into the reaction tube 4 at each boat 12. In this state, the temperature and pressure in the substrate processing chamber 3 are adjusted, and substrate processing gas is then supplied to the substrate processing chamber 3. The substrate processing gas undergoes a reaction due to the heat, and the film-forming components produced by the reaction accumulate on the surfaces of the substrates 23.
For example, in cases in which a gas mixture of SiH2Cl2 and NH3 is supplied as a substrate processing gas to the substrate processing chamber 3, the reaction in the following equation (1) takes place in the substrate processing chamber 3, and Si3N4 (silicon nitride), which is a product of the reaction and which is a film-forming component, accumulates on the surfaces of the substrates 23.3SiH2Cl2+4NH3→Si3N4+6HCl+6H2  (1)
The HCl produced in this reaction bonds with NH3 (ammonium) in a secondary reaction according to the following equation (2) to form NH4Cl (ammonium chloride), which is supplied together with the other reaction components as reaction products and the like from the gas exhaust tube 14 through the exhaust tube 231 to the exhaust trap 8. From the gas used for substrate processing, the exhaust trap 8 recovers the primary components produced by the reaction, the reaction by-products produced by a side reaction among the primary components, and un-reacted components (hereinbelow referred to as reaction by-products and the like) provided in excess of the reaction.NH3+HCl→NH4Cl  (2)
When the exhaust trap 8 undergoes maintenance, the upstream valve 9 and the downstream valve 10 are fully closed, and the exhaust trap 8 is separated from the exhaust tube 231 and washed or subjected to some other maintenance.
The structure of the exhaust trap 8 is shown in FIGS. 12 through 15.
As shown in FIG. 12, a casing 8a of the exhaust trap 8 is configured from an outer tube 8b that is larger in diameter than the outside diameter of the exhaust tube 231, an inner tube 8c inserted in double-tube fashion into the outer tube 8b, and end plates 8d, 8e attached to both ends of the outer tube 8b and the inner tube 8c. A gas inlet tube 55, which passes through the outer tube 8b and inner tube 8c in the radial direction and which is communicated with the interior of the inner tube 8c, is joined to the casing 8a by welding, and a gas exhaust tube 56, which passes through the end plate 8e in the thickness direction and which is communicated with the interior of the inner tube 8c, is joined to the end plate 8e by welding.
In the outer tube 8b of the exhaust trap 8, in order to use the space between the outer tube 8b and the inner tube 8c as a cooling chamber (jacket chamber) 8f to cause reaction by-products and the like to precipitate on the inner surface of the inner tube 8c, a cooling water inlet tube 19 and a cooling water outlet tube 20 are connected to the outer tube 8b. 
Furthermore, a trap main body 17 is housed within the inner tube 8c in order to remove reaction products and the like by means of a cooling surface, similar to the inner tube 8c. The trap main body 17 is attached to an end plate 17b, and the trap main body 17 has a structure that can be attached and removed from the inner tube 8c by attaching and removing the end plate 17b, as shown in FIG. 13.
The structure of the trap main body 17 is described next with reference to FIGS. 12, 13, and 14. The trap main body 17 is configured primarily from a spiral tube (cooling coil) 17a. The inlet 17a1 and outlet 17a2 of the spiral tube 17a pass through the end plate 17b in the thickness direction and are joined to the end plate 17b by welding.
The end plate 17b constitutes a tapered flange that can be attached and removed from a tapered flange 18a at one end of the exhaust trap 8 by means of a coupling (JIS). A spiral shape has a greater surface area than a linear tube and more opportunities to come into contact with reaction by-products and the like, and therefore has the advantage of enabling recovery of more reaction by-products and the like by cooling-induced precipitation.
However, the trap main body 17 is inserted into the inner tube 8c of the exhaust trap 8, cooling water from a cooling water circulation apparatus is passed from the inlet 17a1 of the spiral tube 17a to the outlet 17a2, and reaction by-products and the like in the semiconductor device manufacturing apparatus 1 are actually recovered, whereupon reaction by-products and the like sometimes accumulate primarily in the gas inlet vicinity X of the gas inlet tube 55 of the exhaust trap 8 and in the end plate 8d side Y of the spiral tube 17a, as shown in FIG. 12, and blockage sometimes occurs upstream of the exhaust trap 8.
In view of this, the flow of gas used for substrate processing within the exhaust trap 8 has been simulated, and the cause has been analyzed. The results are shown in FIG. 15. In FIG. 15, the directions of the arrows indicate the flow of gas, and the lengths of the arrows indicate speed. Longer arrows indicate a higher flow rate of gas used for substrate processing, and shorter arrows indicate a lower flow rate.
<Results of Simulation>
(1) When the gas used for substrate processing is introduced into the exhaust trap 8 from the gas inlet tube 55, the flow of gas used for substrate processing changes direction first at one end plate 8d in the vicinity of the connection with the inner tube 8c of the casing 8a, then changes direction towards the opposite side of the entrance of the spiral tube 17a, and then changes direction again in the vicinity of the connection with the gas exhaust tube 56 to be exhausted out to an exhaust tube (hereinafter referred to as the downstream exhaust tube) 231b on the downstream side.
(2) The speed of the gas used for substrate processing is low in the vicinity of the connection between the gas inlet tube 55 and the inner tube 8c, and at the entrance of the spiral tube 17a, and the flow stagnates.
These simulation results (1) and (2) lead to speculation that (a) once precipitated, the reaction by-products and the like more easily precipitate on the precipitation surface, and (b) when the time of contact with the cooling surface (retention time) increases, the amount of precipitated reaction by-products and the like increases proportionately. Conversely, when the contact time decreases, the amount of precipitated reaction by-products and the like also decreases. From these speculations, it is assumed that in a conventional exhaust trap 8, the flow rate is fairly low and the contact time (retention time) is long in the vicinity of connection between gas inlet tube 55 and inner tube 8c of the exhaust trap 8 and at the entrance of the spiral tube 17a. Therefore, reaction by-products and the like in the gas used for substrate processing are precipitated mostly in these two locations, and the reaction by-products and the like cannot be substantially trapped at the downstream side of the spiral tube 17a even in the presence of a capacity to recover the reaction by-products and the like.
In a known example of technology related to this type of exhaust trap, a cartridge is configured from a water cooling tube and a trapping member (Patent Document 1).    Patent Document 1: JP-A 9-202972